Conventionally, in storage devices represented by a magnetic disk device, the floating amount of a head relative to a recording surface of a recording medium such as a magnetic disk must be reduced to achieve high recording density. In recent years, the floating amount of extremely small order has been achieved, e.g., equal to or less than 10 nanometers.
However, when the floating amount of the head is reduced, collisions between the head and minute protrusions on the magnetic disk surface are likely to occur. Further, a clearance between the head and the magnetic disk surface varies for different heads within a mechanical tolerance range. Therefore, when the medium contact is taken into consideration, the floating amount cannot be set lower than the tolerance range.
Accordingly, a method is proposed in which the clearance between the head and the recording surface of the magnetic disk is controlled by incorporating a heater in the head and utilizing the projection phenomenon of the head floating surface caused by thermal expansion when current is supplied to the heater.
In general, the environmental temperature of a storage device is lower than the temperature of the steady state immediately after a recording medium in the storage device starts rotating, for example, when the power of the storage device is turned ON and the storage device starts operating or when the recording medium is returned from the rotation-stopped state, such as a power saving mode, with the power of the storage device already turned ON. Accordingly, it is known that the floating amount of the head in this case becomes higher than the floating amount in the steady state. For example, the floating amount of the head immediately after the start-up of the storage device is approximately 0.4 to 0.6 nanometers higher than the floating amount in the steady state. It is also known that it takes approximately 10 minutes to reach a state, namely, a steady state, in which the storage device can be suitably operated at the values set in advance at the design stage, testing step, and the like.
As mentioned above, immediately after the cold start-up (immediately after the start-up of the device that has been left unpowered or unloaded for a predetermined period of time), write/read characteristics (referred to as start-up characteristics) deteriorate because the floating position of the head comprising elements (writing element and reading element) to which a lubricant agent for the recording medium or the like sticks is elevated. If the start-up characteristics deteriorate to a great extent, the floating position of the head may be elevated by approximately one to two nanometers.
Thus, a method is proposed in which a set value for write current related current (write current (Iw) and overshoot (O/S)) and a set value (read/write heater) for a dynamic flying height (DFH) are adjusted during a fixed period of time immediately after the start-up to prevent the start-up characteristics.
Here, the start-up characteristics must be detected and isolated based on the characteristic deterioration to adjust the set values more effectively. However, the characteristic deterioration is affected by the combination of a medium and head, and the characteristics vary depending on the head. Accordingly, it is difficult to distinguish a head that has deteriorated immediately after the start-up.